Printing machines normally include a printing couple which comprises a number of cylinders and/or rollers such as impression cylinders, master cylinders, blanket cylinders, form rollers, ductor rollers, transfer rollers, regulator rollers, oscillating rollers, and the like. An ink fountain is disposed generally at the rear of the machine for feeding ink to the various rollers of the printing couple which transfers images to copy sheets. In such printing machines as rotary offset lithographic duplicating machines, a moisture fountain also is disposed adjacent the printing couple for feeding moisture to the printing couple. A number of rollers which generally can be termed "distribution" rollers are provided between the ink fountain and/or moisture fountain for distributing ink and/or moisture to the printing couple of the machine.
One of the problems with moisture feeding systems in machines of the character described is the inability to effectively control and/or vary the amount of moisture fed to the printing couple for different or varying printing jobs, such as when different sizes of copy sheets are printed by the machine. When an excessive amount of moisture is fed through the system, the moisture tends to feed back or migrate through the rollers back to the ink fountain and contaminate the ink feeding system. If too little moisture is fed through the system, of course the printing quality will suffer.
Heretofore, the most common expedient for controlling the amount of moisture flow has been to use wipers which usually are located at opposite ends of a distribution roller for wiping or scraping moisture from the surface of the roller. The wipers are very difficult to control and are available in different sizes only in the most elaborate machines. Once a given size wiper is used in a machine, it either is in an "on" mode or an "off" mode and, consequently, there is no easy way to adjust the moisture feed in between the extreme modes. Even when the wipers are in their "on" or operative mode, such varying conditions as atmospheric humidity can greatly affect the moisture flow and, consequently, the copy quality.
This invention is directed to solving the above problems and satisfying a need for a new and improved distribution roller for a moisture system in a printing or duplicating machine wherein the effective surface area of the distribution roller easily can be changed or varied.